Triton is the biggest of Neptune’s thirteen known moons. This moon is suspected to have been captured by Neptune, which would explain its highly unusual orbit and rotation. One of the only bodies in the solar system to have a retrograde orbit, Triton also rotates at an angle of 157° to the axis of Neptune’s rotation. This means that the poles and equator alternately face the sun during rotation, most likely causing dramatic changes in seasons. When the Voyager 2 flew by in 1989, Triton’s South Pole was facing the sun. An ice cap of frozen nitrogen and methane was found on Triton’s South Pole when Voyager 2 visited.

The illusion from which we are seeking to extricate ourselves is not that constituted by the realm of space and time, but that which comes from failing to know that realm from the standpoint of a higher vision. -L.H.

AbstractHubble Space Telescope (HST) observations in August 2002 show that Neptune’s disk-averaged reflectivity increased significantly since1996, by 3.2 0.3% at 467 nm, 5.6 0.6% at 673 nm, and 40 4% in the 850–1000 nm band, which mainly results from dramaticbrightness increases in restricted latitude bands. When 467-nm HST observations from 1994 to 2002 are added to the 472-nm ground-basedresults of Lockwood and Thompson (2002, Icarus 56, 37–51), the combined disk-averaged variation from 1972 to 2002 is consistent witha simple seasonal model having a hemispheric response delay relative to solar forcing of 30 years (73% of a full season).

IntroductionNeptune’s equatorial plane is inclined 29° to its orbitplane, which subjects it to seasonal solar forcing during its164.8-year orbit of the Sun. The resulting local variation inincident sunlight is similar in fractional amplitude to that onthe Earth, but the absolute variation is 900 times smaller andthe rate of change is an additional factor of 165 slower.Remarkably, there is now evidence that Neptune is respondingmeasurably to this weak forcing. A clear trend of increasingbrightness since 1980 has emerged from diskaveragedground-based observations (Lockwood andThompson, 2002) and from spatially resolved Hubble SpaceTelescope (HST) observations in 1996 and 1998 (Sromovskyet al., 2001d). Here we describe new HST observationsin 2002, which confirm a continuing increase inNeptune’s reflectivity and establish new constraints on itsspectral and spatial characteristics. We show that the recentincrease is mainly produced by changes in restricted latituderegions and that the long-term variation follows a simplephase-shifted seasonal model.

Clearlysome variation in Neptune’s spectrum is required to explainthe near-IR results discussed in the previous paragraph.However, it does not seem likely that the effect at shortwavelengths could be large enough by itself to explain theentire discrepancy. Another potential source for unusualbrightness changes is the heightened solar activity near theend of 1957 when the largest-ever monthly mean sunspotnumber was observed (sunspot data from ftp://ftp.ngdc.noaa.gov). Sunspot number was anticorrelated with Neptune’sbrightness during the 1972–1980 period when itseemed to be associated with 2–3% variations in brightness(Lockwood and Thompson, 1986). But during 1950–1961,the B-filter observations of a steadily increasing brightnesscontain no evidence of a 1957 minimum that would havebeen obvious had the same correlation been present then asduring 1972–1980. Thus, the B observations during 1950–1960 seem inconsistent with both seasonal and solar responses.An alternate possibility is that these earlier broadbandmeasurements are in error, either due to instrumentalanomalies or analysis errors. In fact, Jerzykiewicz andSerkowski (1966) themselves raise this issue by pointingout that “The steady decrease of the instrumental coefficientA8 in the years 1950–1960 . . . throws some doubt on thereality of the changes in Neptune’s brightness.” A clearresolution of this discrepancy remains to be found.It should be noted that the discrepancies between theseasonal model and the observations are mainly with observationsthat are minor in effect or made in different spectralbands and that very good agreement is obtained with thebest-calibrated and most spectrally homogeneous diskaveragedobservations. Thus, seasonal forcing remains aplausible explanation for Neptune’s main brightness variation,although a firm understanding of the complete variation andall its contributing factors and spectral variation remains tobe established. Achieving that understanding will probablyrequire a much longer record of observations and moredetailed investigations of physical mechanisms. If the seasonalmodel is correct, Neptune should continue to brightenat 467 nm for almost another two decades.

Maybe someone can find a way of taking some of the images from this PDF. Some could be handy later on.

The illusion from which we are seeking to extricate ourselves is not that constituted by the realm of space and time, but that which comes from failing to know that realm from the standpoint of a higher vision. -L.H.

Previous investigations of sputtering of molecular nitrogen from Triton's atmosphere lead to estimates of escape rates of about 1021 N2 molecules s−1. Here, the erosion of Triton's nitrogen atmosphere resulting from sputtering due to different plasma populations and particles from Neptune's magnetosphere is investigated. This investigation shows that sputtering from Triton's nitrogen atmosphere could lead to N2 escape rates during the plasma sheet crossing on the order of 5 × 1024 s−1. This calculation shows that sputtering of Triton's nitrogen atmosphere by magnetospheric particles is an efficient nonthermal escape mechanism, similar to Saturn's large satellite Titan, and is an additional important process for the power input of the Neptune aurora. The N2 escape rates should be in a good agreement with the measured H+/N+ ion ratio in Neptune's magnetosphere. The excess energy of the sputtered particles leads primarily to escape and supply to the Neptune system rather than to ballistic orbits. Sputtering will yield, however, a small N2 corona on Triton.

The illusion from which we are seeking to extricate ourselves is not that constituted by the realm of space and time, but that which comes from failing to know that realm from the standpoint of a higher vision. -L.H.

Stimulated desorption of atoms and molecules from bodies in the outer solar system

Laboratory data is needed on electronically-induced desorption from low-temperature solids: ices, organics, hydrated salts, glasses and certain minerals. Many bodies in the outer solar system are bombarded by relatively intense fluxes of fast ions and electrons as well as solar UV photons. This can cause both changes in their optical reflectance as well as desorption of atoms and molecules from their surfaces. Stimulated desorption produces Na and K 'atmospheres' above the 'rocky' surfaces of the moon and Mercury and H2O, H2 and O2 'atmospheres' about icy outer-solar system bodies. Since theses bodies contain other surface materials, direct detection by spacecraft or remote detection by telescopes of the desorbed atoms and molecules can be used, along with laboratory data, to determine the surface composition and geological processes occurring on distant bodies. This paper describes the relevance of stimulated desorption to the ambient neutrals and plasma in Saturn's magnetosphere, in preparation for CASSINI's arrival, and to the production of atmospheres on the moons of Jupiter being studied by the Galileo spacecraft.

I Introduction

An exciting period of exploration of the outer solar system is underway by spacecraft, by remarkably improved ground-based observations and by orbiting telescopes: International Ultraviolet Explorer (IUE) and Hubble Space Telescope (HST). These studies have revolutionized our understanding of the solar system revealing a kaleidoscope of unusual worlds. Because of the low surface temperatures, typically < 130K, ice is the 'rock' in the outer solar system. That is, excluding the four giant planets and Io, it is the structural and thermal properties of ice that determines the surface geology of many objects from the orbit of Jupiter outward (Burns and Matthews, 1986). Therefore, understanding the radiation chemistry of and desorption from ice or low-temperature hydrated minerals is critical. Other more volatile molecular species, such as N2, O2, CO, CO2, NH3, CH4, and SO2 form atmospheres and polar 'ices' or can cause the surface to be geologically active. Io, a moon of Jupiter, is an exception. Owing to its tidal interaction with Jupiter, Io is volcanically active and has lost its water and other light volatiles. Because of this, frozen SO2, a volcanic gas on earth, covers Io's surface (Burns and Matthews, 1986).

Since most small, outer solar system bodies, with the exception of Titan, have either no atmospheres or tenuous ones, their icy surfaces are exposed to the solar UV and to the local plasma causing desorption as well as physical and chemical alterations (Johnson, 1990; 1998). During the Voyager I tour of the outer solar system, W.L. Brown, L.J. Lanzerotti and colleagues at AT&T Bell Labs measured the ejection of molecules induced by energetic ion impact of ice. They discovered that the sputtering from low-temperature ices by fast, light ions is determined by the electronic excitations produced in the ice, rather than by knock-on collisions (Brown et al., 1978) and, hence, is an electronically-stimulated-desorption process. This exciting discovery opened a new field of study. Below the relevance of desorption to a few outer solar system bodies is described; for extended descriptions see Johnson (1990; 1996; 1998).

II Desorption from Solar System Bodies

The samples collected during the Apollo missions show the lunar surface is modified by the impacting solar-wind ions (~ 1 keV/u H+ and He++) and by energetic solar particles (Taylor, 1982). This aspect of planetary physics has recently been revived by the observation of Na and K 'atmospheres' around Mercury and the Moon (Potter and Morgan, 1985; 1988). Such atmospheres are produced by stimulated-desorption (the ions, electrons and UV photons) of these atoms from the rocky surfaces (Madey et al. 1998). The sodium atmosphere has been seen to extend to ~ 5 lunar radii from the moon's surface (Flynn and Mendillo, 1993), providing an impressive manifestation of desorption.

Similarly the ions trapped in the Jovian and Saturnian magnetospheres bombard the surfaces of the embedded moons. These ions are energetic (Fig.1) producing a neutral desorption flux of ~ 1011 molecules/cm2/s. Although this is much smaller than typical laboratory sputtering rates, the exposure times are long. The application of laboratory data to the erosion of grains has shown that the icy, main rings of Saturn are transient ( ~ 108 yrs). Of current interest is a ring of micron-sized ice grains called the E-ring, lying outside the main rings in the region where the plasma trapped in Saturn's magnetosphere is relatively intense. Desorption rates based on laboratory data (Shi et al., 1995) place an upper limit on the survival of these charged ice grains (Jurac et al. 1995) of about 1000 years. Therefore, the E-ring must have a source, presumably a relatively recent massive impact or volcanic activity on the moon Enceladus

The illusion from which we are seeking to extricate ourselves is not that constituted by the realm of space and time, but that which comes from failing to know that realm from the standpoint of a higher vision. -L.H.

Abstract. We examine the plausible existence of Neptune's plasmasphere- and study the drift ofparticles inside it. Using the 08 magnetic field model [Comemey et aZ., 19911 and assuming auniform solar wind convection electric field, the plasma convection time and refilling time arecalculated in a Euler potential coordinate syste[mH o et aL, 19971. The plasma density and refillingtime at the equilibrium state are first calculated, and the location of the plasmapause is set to bewhere the refilling time and convection time are equal. The refilling time as a function of ion speedis then recalculated along field lines, and the plasma density and temperature are obtained bydirectly integrating the local ion distribution function over the range of speeds for which therefilling time is less than the convection time. The density calculated using this model shows sharpdrop-offs at approximately 3.25 to 4.5 RN on the zero magnetic scalar potential surface, aboundary taken to be the plasmapause. Our calculated density compares fairly with the observeddensity along the Voyager trajectory within about 5 RN. Ion temperature is also calculated along thefield line with results which indicate that high-speed tails of the distribution function might beneeded to explain the high observed temperature measured along the Voyager 2 trajectory. Drifttrajectories and speeds of 90" pitch angle particles inside the plasmapause are calculated. Particlesof energy above tens of eV are gradient drift dominated, and the drift paths of this class of particlesare essentially the minimum B contours that are similar to Acuiia et aZ.'s [1993] calculations.Atmospheric precipitation otfh e J = 0 particles may provide an explanation for the UV emissions,as an alternative to the "monoprecipitation" suggested by Puranicas and Cheng [ 19941. Drifts oflow-energy particles are strongly affected by the gravitational andc entrifugal forces, and becauseof the largely tilted dipole and the large higher components of magnetic field, the resultant drift isnonaxisymmetric and quite complicated.

According to Ness et d ' s [ 1989] OTD (Offset Tilted Dipole) model, Neptune has a dipoleaxis tilted about 47" from the rotation axis. Together with the 113" angle the rotation axis madewith the Neptune-Sun direction during the Voyager 2 flyby to the planet, the large tilted angleresults in an “Earth-like” and a “pole-on” magnetic field configurations at two extreme positionsduring each revolution of the planet as the rotation axis, the dipole axis and the Neptune-Sundirection all lie in the same plane [Ness et al., 1989; Selesnick, 19901. These two extremepositions represent the upper and approximately the lower limits of the efficiency of couplingbetween the solar wind and the convection over the polar cap, and the strong modulation of theconvection electric field in the Neptunian magnetosphere causes a cumulative effect like theacceleration of particles in a cyclotron[S elesnick, 19901.

Since Neptune has an Earth-like position and Earth has a plasmasphere, and while in thepole-on position, solar wind magnetosphere coupling at Neptune this is weakest and the likelihoodto form a plasmasphere is highest, Neptune should also have a plasmasphere. The existence of aplasmasphere at Neptune is also supported by the Voyager 2 Plasma Wave Instrument (PWS),which detected whistler signals with large dispersions [Gurnett et aZ., 19891 that require denseplasma path lengths along field lines.

Further arguments for the existence of a Neptunian plasmasphere can be made as follows:Neptune has a region, extended to about three planetary radii (1 RN = 24,765 km), dominated bythe gravitational force, and in this region the ionospheric plasma refilling surpasses the solar winddriven convection,L emaire [1974] has used the critical distance, “Roche Limit,” beyond which therefilling time quickly increases, to define Earth’s plasmapause. Earth’s plasmasphere defined inthis way has a size of 5.8 RE, a value not too far from the actual observed average values. ForNeptune, assuming a spin axis-aligned dipole as a rough estimate, the critical distance of Neptuneis 3 RN. However, because of the larger gravity and the lower ionospheric temperature of Neptune[Tyler et aZ., 19891, the plasma distribution in the plasmasphere differs from that of the terrestrialplasmasphere in that the plasma density gradient along a field line from the ionosphere to theequatorial plane is quite large. As a result of the low plasma density of ionospheric origin along thefield line in the low magnetic latitude region, the incoref a spela sma refilling time with increasing Lshell is not so fast as in the terrestrial magnetosphere, and hence the actual size of the Neptunianplasmasphere might be larger than the above estimate of at 3 RN.

In this paper, based on the competition of plasma. refilling with the solar wind drivenconvection, we construct a model of plasmasphere at Neptune. We also study the particle driftmotions inside the plasmasphere. The magnetic field model we use of are various calculations is the08 model [Connerney et al. 19911, and for representing it the a and p (Euler potentials)coordinates [Ho et al., 19971 are used. The 08 model, including the dipole, quadrupole andoctupole of the field, has been used to study field geometry invariants d arnifdt shells [Acuiia et al.,19931, and aurora in association with W emissions [Puranicasa nd Cheng, 19941.

This paper is structured as follows. In section 2, we calculate the plasma densityoriginating from the ionosphere, assuming an equilibrium state, i.e., a full Maxwellian distributioneverywhere on the concerned field lines. We then proceed by comparing the solar wind drivenconvection time with the plasma refilling time to estimate the size of the plasmasphere, as anapproximation. Next, for a more accurate calculation, we consider the local dynamic accessibilityof particles in the refilling process.T his is followed by a more meticulous study of the dynamics ofions along the field lines. To do this, we calculate the refilling time of the ions that can access acertain point on a field line. By integrating the local ion distribution functoiovne r the rangeo f ionspeeds that correspond to a refilling time less than the convection time, the ion density andtemperature can be obtained. The location of the plasmapause is thus determined to be where thedensities show sudden drop-offs. In section 3, we compare the calculated plasma densities andtemperatures witht he Voyager Plasma Science Experiment (PLS) measurements. In secti4o,n w ecalculate the particle drift paths and drift velocities inside the plasmasphere of Neptune. Finally,discussion and conclusions are given in section 5.

5. Discussion and ConclusionsBased on the fact that the refilling time of the ionospheric ions is less than the solar winddriven convection time within a few planetary radii, we set out to argue for the existence of aplasmasphere at Neptune and proceeded to estimate its size, density, and temperature. Theexistence of a plasmasphere at Neptune is supported by the fact that Voyager2 PWS detected largedispersive Whistler waves, suggesting large densities along field lines. Other evidence is the lackof report on the day-night asymmetries in plasma density. Such density asymmetries have beenused as an argument for a convection-dominated magnetosphere at Uranus. In the case of Uranus,convection domination, and hence the lack of a plasmasphere ,may be supported by the theoreticalargument that solar wind particles can penetrate easily into the inner magnetosphere because of thenear alignment of the spin axis and the solar wind flow. The penetration, however, may not beachieved so readily if the inner flux tubes are filled by interhemispherical plasma flow in atimescale that is short compared to the convection time, in fact, sharp plasma edges were observedat Uranus which may be explained by the reduction of the electric field in the inner region that thusprovides some sort of "shielding" [WoZf, 19831. The method used in this paper can be applied toUranus to determine if it has a plasmasphere.

In the first approximation, the plasma was assumed to be in an equilibrium state, and theboundary at which the plasma refilling time equals the solar wind driven convection time is taken tobe the plasmapause.The plasmasphere so obtained has a size of about 7 planetary radii on the zeromagnetic scalar potential surface, which is obviously overestimated, indicating an equilibrium stateof plasmaspheric plasma to be a poor assumption.

In more accurate calculations, we have taken the effect of accessibility of ions from theionosphere to a certain point on a field line due to both the potential barrier resulting from thegravity and centrifugal force and the requirement of the local refilling time to be less than the solarwind driven convection time. By calculating the time to fill a flux tube from the ionosphere to aspecific point on the field line for the ions which are able to cross the potential barriers andcomparing with the convection time, the accessibility of the ionospheric ionso f various speeds tothat particular point was determined.The density and temperature of the plasma at the local pointwere then obtained by integrating over all the ions that are accessible to the concerned point. Bythis we found that Neptune has a plasmasphere which has its boundary located between3 .25 and4.5 RN on the zero magnetic scalar potential surface.

The calculated H+ densities and temperatures/ were compared with the Voyager 2observations. The measured density minima at about 3 RN inbound and 5 RN outbound wereroughly the location of the plasmapause we calculated. The plasma density drops exponentiallywith distance inside the plasmasphere because of the large gravity of Neptune, and the suddendensity drop-offs at the plasmapause we calculated have magnitudes a few orders lower than theionospheric density. The Neptunian plasmasphere is therefore quite different from Earthsplasmasphere, which has a density that does not decrease appreciably with distance until the dropoffat the plasmapause. The high temperatures observed may result from the high-speed tails of theions escaping from the ionosphere. Other sources of plasmas such as solar wind particles andplasmas originating from Neptune's moons and rings, as well as various heating processes, mayalso contribute to the measured bulk plasma parameters.

We also calculated the particle drifts. Only 90" pitch angle particles are considered in thispaper, which simplifies the problem to two-dimensions by removing bounce motions.D ue to thehigh nondipole magnetic components, particles very near the planed to not execute complete 360"drifts, similar to Acuiia et aZ.'s E19931 results given on the minimum B contours. Energetic 90"pitch angle particles precipitate into the atmosphere along them agnetic equator on the planetarysurface, providing an alternate explanation for Paranicas and Cheng's [ 1 9941 "monoprecipitation."In the range of 2 - 4 RN, particles of energies of 100 eV and above drift at the speeds that arecomparable to the solar wind driven convection speeds, of the order of a few m/s . The drifts ofparticles of lower energies are strongly affected by the gravitational and centrifugal forces, andconstrained to the surfaces where the first invariant of the particles is maximum on each field

The illusion from which we are seeking to extricate ourselves is not that constituted by the realm of space and time, but that which comes from failing to know that realm from the standpoint of a higher vision. -L.H.

The 17 large and medium-size satellites of the outer planets, shown to scale, are worlds in theirown right. The Galilean satellites of Jupiter (top row) are (from left) Io, whose surface is constantly renewed by activevolcanoes tinged with sulfur allotropes; Europa, which probably possesses a liquid water ocean beneath its ruddy ice skin;Ganymede, a moon bigger than the planet Mercury, possessing a rutted surface of dirty ice and an internally generatedmagnetic field; and Callisto, a moon with an ancient cratered surface whose interior is only weakly differentiated. Saturn’sfamily of bright icy moons (second row) consists of Mimas, Enceladus, Tethys, Dione, and Rhea; cloud-shrouded Titan hasan atmosphere rich in organics and possibly seas of methane; and two-toned Iapetus shows one face as bright as snow and theother as black as coal. The five major uranian satellites (third row) are Miranda, Ariel, Umbriel, Titania, and Oberon. Eachdisplays a dirty-ice surface and some tectonic activity, but the bizarre world of Miranda—with its exotic jumble of surfaceterrains suggesting that it may have been totally disrupted in the past and put back together at random—steals the show.Neptune’s sole large satellite (fourth row), Triton, is coated with exotic ices tinged pink by organic molecules; nitrogengeysers spew high into its tenuous atmosphere. Courtesy of NASA/JPL.

Of the six large outer-planet satellites—Io, Europa, Ganymede, Callisto, Titan, and Triton—all are larger thanPluto and two are larger than Mercury; in addition, there are 11 medium-sized satellites (Figure 5.1; Table 5.1).Each planet-sized satellite is unique:• Io is intensely volcanically active,• Europa may have a layer of subsurface water greater in volume than all of Earth’s oceans combined,• Ganymede has an intrinsic magnetic field,• Callisto is largely undifferentiated,• Titan has a thick atmosphere rich in organic compounds, and• Triton has active, geyserlike eruptions.The large satellites have bizarre life cycles, influenced by orbital evolution and tidal heating, revolutionizingconcepts based on the terrestrial planets. They are rich in volatile species such as H2O, SO2, N2, CH4, CO2, andperhaps NH3, creating a rich diversity of processes and environments. The 11 medium-sized satellites are alsounique worlds, and they may provide essential information about the origin and evolution of satellite systems.

WHY DO WE CARE ABOUT LARGE SATELLITES?Why are these large satellites worthy of national and international exploration and research? One good reasonis that advancing basic research about physical processes in fields such as volcanology and meteorology mayeventually provide benefits that will improve our lives. Another is that such interesting worlds inspire our youthand students to excel in mathematics and science. But the most compelling motivation is to understand the originand destiny of life. Water is essential to life as we know it, and the large icy satellites may contain the largestreservoirs of liquid water in the solar system. Outside Earth, Europa may be the best place in the solar system tosearch for extant life. Titan provides a natural laboratory for the study of organic chemistry over temporal andspatial scales unattainable in terrestrial laboratories. Perhaps teeming with life or perhaps sterile today, theseworlds do contain the basic ingredients for life. Knowing whether they do or do not harbor life is equallyimportant. The origin and evolution of satellite systems also provide analogs for understanding extrasolar planetaryand satellite systems, some of which may be abodes for life.

TritonFour separate ices have been identified spectroscopically on Triton’s surface: N2, CH4, CO, and CO2.43,44The latter three species (except perhaps CO2) exist partially in solid solution with N2, the main constituent. Morecomplex organic molecules are also expected to be present as a result of photolysis and radiolysis. Triton’s surfacetemperature of approximately 38 K creates an atmosphere in vapor pressure equilibrium with the ices, which ishighly responsive to heating changes associated with solar insolation and the variable photometric and compositionalproperties of the surface. As a result, the atmosphere experiences large-scale sublimation, transport, andrecondensation of N2, CO, and CH4. Another unique characteristic is Triton’s geyserlike plumes that entrain darkdust and rise 8 km above the surface.45 A diffuse haze pervades the atmosphere; it probably consists of thecondensation of hydrocarbons created by photochemistry. Discrete clouds, likely condensed N2, are present nearthe poles.

Magnetospheric Processes and Interactions

Sputtering/Implantation

The large satellites of the gaseous giant planets spend all or most of their time in the corotating magnetospheresof these planets. The interaction of satellite and corotating plasma modifies the satellites’ surfaces andatmospheres and leads to a net loss of volatile materials to the magnetospheres. At the present time, Io is knownto lose more than a ton per second of volatile material (mostly S and O) to Jupiter’s magnetosphere.51 Similarly,Europa is losing its icy surface at the rate of ~2 cm per million years (Myr) to Jupiter’s magnetosphere.52Ganymede’s magnetic field partially shields the equatorial regions from plasma bombardment. However, it isestimated that the polar regions of Ganymede lose an average of 8 mm/Myr of ice from sputtering.53 Callisto, ina more benign radiation environment, loses <0.4 mm/Myr of ice to sputtering. The plasma bombardment of icysurfaces results in the implantation of S derived from Io’s torus into the crusts of icy satellites.54 The irradiationof icy satellite surfaces also results in the production of H2, O2, H2O2, and other stable oxides that get embeddedin the ices and also form tenuous atmospheres near the surface.55 The irradiation of other ice contaminants suchas C and S produces CO2, SO2, and H2SO4. The radiolysis of the surface by magnetospheric particles continuouslycycles S between SO2, H2SO4, and polymer S forms.56 At Europa, the fast recycling of the crust (believed to occurover a time scale of 100,000 to 10 million years) may deliver oxidants from the surface to the subsurface ocean.57These oxidants could fuel life in the absence of sunlight.

Style of Plasma Interaction

The type and strength of satellite/magnetospheric interaction depends on the satellite’s size, surface composition,and electrical conductivity, the presence or absence of an internal magnetic field in the satellite, and thedensity, composition, and speed of the interacting plasma. Based on these factors, three distinct types of interactionshave been observed. In the nonconducting type of satellite/plasma interaction, as in the case of Callisto,the magnetospheric plasma slams into the satellite and is absorbed, but sputters some volatile material off thesatellite’s surface.A second type of interaction, called the conducting-satellite/plasma interaction, is best illustrated by Io andEuropa. Because of a well-developed ionosphere at Io and large plasma pickup near Europa, most of themagnetospheric plasma is diverted around the moons. Only a small fraction of the incoming plasma flux strikesthe moons and sputters volatile materials off the surface. The strong Alfvén wing currents generated in theinteraction are closed in the ionosphere of Jupiter where they generate visible footprints (see Figures 4.3 and 4.4).The third type of interaction is epitomized by Ganymede, which generates its own internal magnetic field.58Ganymede’s magnetic field is strong enough that it creates a minimagnetosphere of its own in Jupiter’s magnetosphere,partially shielding the satellite from plasma bombardment. The interaction between Ganymede’s magnetosphereand Jupiter’s magnetosphere is similar to the interaction between Earth’s magnetosphere and the solarwind, in which magnetic reconnection plays a key role.Curiously, the other three Galilean satellites were found not to have internal fields at present. However, it islikely that some or all of the other large moons of the solar system were endowed with an internal magnetic fieldat some time in their evolution.

Induced Fields

Europa, Ganymede, and Callisto. Magnetic observations from the vicinities of Europa, Ganymede, and Callistoshow that all three moons generate electromagnetic induction fields in response to the rotating field of Jupiter.59,60 Themagnetic signatures are consistent with the presence of subsurface electrically conducting shells in these bodies.Detailed analyses for Europa and Callisto suggest that liquid subsurface oceans with thicknesses exceeding a fewkilometers could account for the enhanced subsurface conductivities.61 Geological and geophysical lines ofevidence are consistent with liquid subsurface oceans within Europa and Ganymede. However, the presence ofelectromagnetic induction from geologically inactive Callisto was indeed a surprise.Titan. The only spacecraft to make in situ observation of the interaction of Titan with Saturn’s magnetosphere wasVoyager 1, which flew through the plasma wake of Titan. No appreciable internal magnetic field was observed(surface field strength <30 nT).62 The main pickup ion is N+, and the integrated surface pickup rate is ~1024 ionsper second. The geometry of the flyby was not suitable to infer the presence or absence of an electromagneticinduction signature, so magnetic measurements cannot yet speak to the question of an ocean within Titan.

UNIFYING THEMES AND KEY SCIENTIFIC QUESTIONSFOR LARGE SATELLITE EXPLORATIONThe Large Satellites Panel evaluated and organized key scientific questions around four major themes that, inits opinion, best capture the most important scientific questions pertinent to large satellites. They are as follows:• Origin and evolution of satellite systems. Tidal heating and orbital evolution have led to complex historiesfor some large satellites. Satellite systems may form and evolve in ways analogous to planetary systems but aremuch more accessible for detailed study than are extrasolar planetary systems.• Origin and evolution of water-rich environments in icy satellites. Evidence for water within the icyGalilean satellites has led to a new paradigm for the potential habitability of planetary systems. Europa offers thegreatest potential for finding life, because the subsurface water may interact with the surface and the silicate mantle.• Exploring organic-rich environments. Although organic materials are common in the solar system, onlyEarth and Titan allow the study of organic chemistry in the presence of a thick atmosphere, a solvent, and a solidsurface. Titan may enable study of the conditions leading to the origin of life.• Understanding dynamic planetary processes. We can best understand physical processes by observingthem in action, and satellites such as Io, Titan, and Triton offer a broad range of current activity, from the interiorsto the surfaces, atmospheres, and magnetospheres

The illusion from which we are seeking to extricate ourselves is not that constituted by the realm of space and time, but that which comes from failing to know that realm from the standpoint of a higher vision. -L.H.

As a bonus to science, researchers Marcus Knudson, Mike Desjarlais, and Daniel Dolan discovered a triple point at which solid diamond, liquid carbon, and a long-theorized but never-before-confirmed state of solid carbon called bc8 were found to exist together.

“Liquid carbon is electrically conductive at these pressures, which means it affects the generation of magnetic fields,” says Desjarlais. “So, accurate knowledge of phases of carbon in planetary interiors makes a difference in computer models of the planet’s characteristics. Thus, better equations of state can help explain planetary magnetic fields that seem otherwise to have no reason to exist.”

When the comet Shoemaker-Levy 9 hit Jupiter sixteen years ago, scientists all over the world were prepared: instruments on board the space probes Voyager 2, Galileo and Ulysses documented every detail of this rare incident. Today, this data helpsThe "dusty snowballs" leave traces in the atmosphere of the gas giants: water, carbon dioxide, carbon monoxide, hydrocyanic acid, and carbon sulfide. These molecules can be detected in the radiation the planet radiates into space.

In February 2010 scientists from Max Planck Institute for Solar System Research discovered strong evidence for a cometary impact on Saturn about 230 years ago (see Astronomy and Astrophysics, Volume 510, February 2010). Now new measurements performed by the instrument PACS (Photodetector Array Camera and Spectrometer) on board the Herschel space observatory indicate that Neptune experienced a similar event. For the first time, PACS allows researchers to analyze the long-wave infrared radiation of Neptune.

The atmosphere of the outer-most planet of our solar system mainly consists of hydrogen and helium with traces of water, carbon dioxide and carbon monoxide. Now, the scientists detected an unusual distribution of carbon monoxide: In the upper layer of the atmosphere, the socalled stratosphere, they found a higher concentration than in the layer beneath, the troposphere. "The higher concentration of carbon monoxide in the stratosphere can only be explained by an external origin", says MPS-scientist Paul Hartogh, principle investigator of the Herschel science program "Water and related chemistry in the solar system". "Normally, the concentrations of carbon monoxide in troposphere and stratosphere should be the same or decrease with increasing height", he adds.

The only explanation for these results is a cometary impact. Such a collision forces the comet to fall apart while the carbon monoxide trapped in the comet’s ice is released and over the years distributed throughout the stratosphere. "From the distribution of carbon monoxide we can therefore derive the approximate time, when the impact took place", explains Thibault Cavalié from MPS. The earlier assumption that a comet hit Neptune two hundred years ago could thus be confirmed. A different theory according to which a constant flux of tiny dust particles from space introduces carbon monoxide into Neptune’s atmosphere, however, does not agree with the measurements.

In Neptune’s stratosphere the scientists also found a higher concentration of methane than expected. On Neptune, methane plays the same role as water vapor on Earth: the temperature of the socalled tropopause - a barrier of colder air separating troposphere and stratosphere - determines how much water vapor can rise into the stratosphere. If this barrier is a little bit warmer, more gas can pass through. But while on Earth the temperature of the tropopause never falls beneath minus 80 degrees Celsius, on Neptune the tropopause's mean temperature is minus 219 degrees.

Therefore, a gap in the barrier of the tropopause seems to be responsible for the elevated concentration of methane on Neptune. With minus 213 degrees Celsius, at Neptune’s southern Pole this air layer is six degrees warmer than everywhere else allowing gas to pass more easily from troposphere to stratosphere. The methane, which scientists believe originates from the planet itself, can therefore spread throughout the stratosphere.

Still I think, although I couldn't quite trace the argument shooting down the influx from outside-hypothese, that there is is room for sputtered material migrating from for instance Triton to flow and seed the stratosphere of Neptune. This in relation with:

TritonFour separate ices have been identified spectroscopically on Triton’s surface: N2, CH4, CO, and CO2.43,44The latter three species (except perhaps CO2) exist partially in solid solution with N2, the main constituent. Morecomplex organic molecules are also expected to be present as a result of photolysis and radiolysis. Triton’s surfacetemperature of approximately 38 K creates an atmosphere in vapor pressure equilibrium with the ices, which ishighly responsive to heating changes associated with solar insolation and the variable photometric and compositionalproperties of the surface. As a result, the atmosphere experiences large-scale sublimation, transport, andrecondensation of N2, CO, and CH4. Another unique characteristic is Triton’s geyserlike plumes that entrain darkdust and rise 8 km above the surface.45 A diffuse haze pervades the atmosphere; it probably consists of thecondensation of hydrocarbons created by photochemistry. Discrete clouds, likely condensed N2, are present nearthe poles.......Magnetospheric Processes and Interactions

Sputtering/Implantation

The large satellites of the gaseous giant planets spend all or most of their time in the corotating magnetospheresof these planets. The interaction of satellite and corotating plasma modifies the satellites’ surfaces andatmospheres and leads to a net loss of volatile materials to the magnetospheres. At the present time, Io is knownto lose more than a ton per second of volatile material (mostly S and O) to Jupiter’s magnetosphere.51 Similarly,Europa is losing its icy surface at the rate of ~2 cm per million years (Myr) to Jupiter’s magnetosphere.52Ganymede’s magnetic field partially shields the equatorial regions from plasma bombardment. However, it isestimated that the polar regions of Ganymede lose an average of 8 mm/Myr of ice from sputtering.53 Callisto, ina more benign radiation environment, loses <0.4 mm/Myr of ice to sputtering. The plasma bombardment of icysurfaces results in the implantation of S derived from Io’s torus into the crusts of icy satellites.54 The irradiationof icy satellite surfaces also results in the production of H2, O2, H2O2, and other stable oxides that get embeddedin the ices and also form tenuous atmospheres near the surface.55 The irradiation of other ice contaminants suchas C and S produces CO2, SO2, and H2SO4. The radiolysis of the surface by magnetospheric particles continuouslycycles S between SO2, H2SO4, and polymer S forms.56 At Europa, the fast recycling of the crust (believed to occurover a time scale of 100,000 to 10 million years) may deliver oxidants from the surface to the subsurface ocean.57These oxidants could fuel life in the absence of sunlight.

blobs of material that rise from depth and penetrate through a surface layer. This suggests that Triton's crust is layered. Some of the smooth deposits at right may be volcanic in origin. Plumes (or Geysers) One of the biggest surprises about Triton was the discovery of atmospheric plumes in the spotted southern hemisphere of Triton. These plumes reach heights of 8 kilometers and are blown laterally by winds in the extremely thin atmosphere (!). They can be traced for several hundred kilometers. The origin of these plumes is still a matter of debate. They may be the result of solar heating of a thin frozen nitrogen layer, or of melting of volatiles near the surface by internal heat.

Hubble also spied two small satellites, named Mab and Cupid. One of the satellites shares an orbit with the outermost of the new rings. The satellite is probably the source of fresh dust that keeps replenishing the ring with new material knocked off the satellite from meteoroid impacts. Without such replenishment, the dust in the ring would slowly spiral in toward Uranus. Collectively, these new discoveries mean that Uranus has a youthful and dynamic system of rings and moons......."We think that dusty rings in general are sustained by impacts," de Pater said. "The rings of Jupiter exist because small meteorites continuously bombard the moons in Jupiter's system."Study co-author Heidi Hammel of the Space Science Institute in Ridgefield, Connecticut, added that Uranus has been "the unappreciated underdog of the outer solar system for too long."It is refreshing to see such dynamic change and exciting evolution in the rings and the planet."

The maps show evidence for asymmetrical patterns, due tothe existence of CO jets. Analysis of the spectra and their velocity shifts shows thatthere is a spiral CO jet rotating in a plane almost perpendicular to the sky plane.This is the rst time that rotating jets are observed for parent molecules. We havedeveloped a 3-D model simulating rotating spiral jets of CO gas......

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Thrill seekers may want to hitch a ride on the giant comet Hale-Bopp, but they would fail vehicle emission tests miserably. When it was the same distance from the Sun as Earth, Hale Bopp produced carbon monoxide (CO) emissions equal to that given off by 5.5 billion cars every day.

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a puzzle about the nature and distribution of elemental carbon and carbonaceous material in its nucleus and coma. The nucleus is darker even than coal (albedo <4%)1, suggesting that its volatile ices contain a few per cent of carbonaceous material in the form of graphitic or amorphous carbon.The very high abundance of light elements in the coma dust2, 3, particularly H, C, N and O, suggests the presence of a significant organic component. The emission feature near 3.4 m also implies the presence of organic material in the dust 4–6. But the parent species for the primary carbon-containing material that have been identified so far (such as CO, CO2 and CH4) are not present in sufficient quantities to account for all of it. Here we propose that an additional contribution from carbon suboxide (C3O2) in the coma dust and the nucleus material is consistent with the observational data

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Jupiter's atmosphere still contains remnants of a comet impact from a decade ago, but scientists said last week they are puzzled by how two substances have spread into different locations........The highest concentration of carbon dioxide, however, has shifted away from the latitude of the impact. It is most prevalent poleward of 60 degrees south and decreases abruptly, toward the equator, north of 50 degrees south. Another smaller spike in its presence occurs at high northern latitudes, around 70 to 90 degrees north.Perhaps the two chemicals got distributed at different altitudes, and are being moved around by different currents, Flasar told SPACE.com. Or maybe the formation of the carbon dioxide was more complex than thought. He said it might have involved carbon monoxide first moving away from the impact area and then interacting with other substances at higher latitudes before being converted to carbon dioxide.

So there is the presence of CO and CH4 and all such as named above, are possible to get from sputtering whether from comets,moons or asteroids. Even mixing of these compounds on gasgiants are not as predictable as was thought. Etc, etc......

The illusion from which we are seeking to extricate ourselves is not that constituted by the realm of space and time, but that which comes from failing to know that realm from the standpoint of a higher vision. -L.H.

Still I think, although I couldn't quite trace the argument shooting down the influx from outside-hypothese, that there is is room for sputtered material migrating from for instance Triton to flow and seed the stratosphere of Neptune.

I think it proves that these scientists are not required to sit in the same rooms with each other and talk, read each other's work, or in any other way attempt to stay current with other discoveries in not only other disciplines, but with the work that others are doing with the same satellite!

One guy is adamant about this material only being able to be brought in via the 'Comet Express', while others are taking measurements on the amount of sputtered material they are observing transiting the two bodies... rediculous. Yet- even the guys who are measuring the material being sputtered off the moons is careful to avoid mentioning HOW sputtering occurs in the first place!

Meh.

Mike H.

"I have no fear to shout out my ignorance and let the Wise correct me, for every instance of such narrows the gulf between them and me." -- Michael A. Harrington

"Astronomers have observed a gigantic storm on Neptune so big it covers an area the size of Earth while testing a telescope on Hawaii.

"The huge storm is about 9,000 kilometres in length, or one-third the size of Neptune's radius.It spans at least 30 degrees in both latitude and longitude, and was spotted during a dawn test run of a Hawaii observatory.

"While observing Neptune at dawn with the Keck Telescope, the nearly circular storm system near Neptune's equator, a region where astronomers have never seen a bright cloud, was spotted. The centre of the storm complex is 9,000 km across, about 3/4 the size of Earth, or 1/3 of Neptune's radius.

"The test was designed to test if telescopes could still provide useful information during twilight.

"Traditionally, astronomers wait until dark to begin observations.

"'Seeing a storm this bright at such a low latitude is extremely surprising,' said Ned Molter, a UC Berkeley astronomy graduate student, who spotted the storm complex near Neptune's equator during a dawn test run of twilight observing at W. M. Keck Observatory on Maunakea, Hawaii.

"'Normally, this area is really quiet and we only see bright clouds in the mid-latitude bands, so to have such an enormous cloud sitting right at the equator is spectacular.'

"This massive storm system was found in a region where no bright cloud has ever been seen before.

"Researchers observed it getting much brighter between June 26 and July 2.

"'Historically, very bright clouds have occasionally been seen on Neptune, but usually at latitudes closer to the poles, around 15 to 60 degrees north or south,' said Imke de Pater, a UC Berkeley professor of astronomy and Molter's adviser.

"'Never before has a cloud been seen at or so close to the equator, nor has one ever been this bright.'

"Images of Neptune taken during twilight observing revealed an extremely large bright storm system near Neptune's equator (labelled 'cloud complex' in the upper figure), a region where astronomers have never seen a bright cloud. The centre of the storm complex is ~9,000 km across, about 3/4 the size of Earth, or 1/3 of Neptune's radius. The storm brightened considerably between June 26 and July 2, as noted in the logarithmic scale of the images taken on July 2.

"At first, de Pater thought it was the same Northern Cloud Complex seen by the Hubble Space Telescope in 1994, after the iconic Great Dark Spot, imaged by Voyager 2 in 1989, had disappeared.

"But de Pater says measurements of its locale do not match, signaling that this cloud complex is different from the one Hubble first saw more than two decades ago.

"When its temperature drops below the condensation temperature of a condensable gas, that gas condenses out and forms clouds, just like water on Earth.

"NASA's Voyager 2 spacecraft gave humanity its first glimpse of Neptune and its moon Triton in the summer of 1989. This picture of Neptune was produced from the last whole planet images taken through the green and orange filters on the Voyager 2 narrow angle camera. The picture shows the Great Dark Spot and its companion bright smudge; on the west limb the fast moving bright feature called 'Scooter' and the little dark spot are visible.

"On Neptune we expect methane clouds to form.

"As with every planet, winds in Neptune's atmosphere vary drastically with latitude, so if there is a big bright cloud system that spans many latitudes, something must hold it together, such as a dark vortex.

"Otherwise, the clouds would shear apart.

"'This big vortex is sitting in a region where the air, overall, is subsiding rather than rising,' said de Pater.

"'Moreover, a long-lasting vortex right at the equator would be hard to explain physically.'

"If it is not tied to a vortex, the system may be a huge convective cloud, similar to those seen occasionally on other planets like the huge storm on Saturn that was detected in 2010.

"Although one would also then expect the storm to have smeared out considerably over a week's time.'This shows that there are extremely drastic changes in the dynamics of Neptune's atmosphere, and perhaps this is a seasonal weather event that may happen every few decades or so,' said de Pater."